Eradication of Aquatic Insects in Rearing Ponds

• Insects usually found in large numbers in ponds over the greater part of the year, especially during and after rains.
• They injure the spawn and some of them prey upon spawn.
• Hence, the insects should be eradicated prior to stocking to ensure maximum survival of the spawn.
• Aquatic insects and their larvae compete for food with the young fish.
• They cause large-scale destruction of hatchlings in nurseries.
• Common aquatic insects found in nursery ponds are Notonecta, Ranatra, Cybister, Lethoceros, Nepa, Hydrometra and Belostoma are highly destructive to the carp seed.

Controlling methods of aquatic insects

• The spraying of oil emulsion is 12-24 hours before stocking the spawn in nursery pond so as to eradicate the insects.
• The oil emulsion with 60 kg of oil and 20 kg soap are sufficient to treat one hectare of water.
• The soap is dissolved first in water and it is added to the oil and stirred thoroughly to get a brownish grey solution. It is then spread on the surface of the water. All the aquatic insects die because of suffocation due to the thin oil film on the surface of the water. The spiracles of insects are closed by the oily film so that they die.
• An emulsion of 56 kg of mustard oil and 560 ml of Teepol is also useful to treat one hectare of water.
• An emulsion can also be prepared with diesel boiler oil and any detergent.
• 50 cc of Hyoxyde-10 mixed in 5 litres of water with 50 litres of high speed diesel oil for a hectare of water.
• The mixture of Herter W.P (0.6-1.0 ppm) and oil extracted from plant Calophyllum inophyllum is effective to insects as well as prawns like Paleamon lamenii, which is usually found in nurseries.
• A mixture of 0.01 ppm gamma isomer of benzene hexachloride and ethyl alcohol is also highly toxic to insects.
• Application of biodegradable  organophosphates like Fumadol, Sumithion, Baytex, Dipterex, etc. (0.25 to 3 ppm) are useful to kill the insects.
• Whenever an oil emulsion is applied, there should be no wind as it disturbs the oil film, and its effectiveness will not be felt on the eradication. Birds like king fishers, herons and cormorants are destructive to fry and fish. Thin lines stretched across the pond are the most effective means of controlling them.
• Kerosene @100-200 l or diesel @75 l and liquid soap @ 560 ml or detergent powder @ 2-3 kg per hectare water area can be used as substitute to make the emulsion.